Underground shale retorting process



July 30, 1957 w, SCOTT, JR I 2,801,089

UNDERGROUND SHALE REITORTING PROCESS Filed March 14, 1955 3 Sheets-Sheet 2 w a 2 5 T o (I O k B v a a m g m m I\ u: i T w j v I; f b 3 5/ o o, \si

Es 5 INVENTOR JOHN W. SCOTT, JR.

1 a may I ATTORNEYS i x N m 0 fig]? u.

July 30, 1957 J. w. scoTT, JR 2,801,089

UNDERGROUND SHAhE RETORTING PROCESS Filed March 14, 1955 s sheets-sheet 3 $86 $86 I I & --A|R as 7 r OVERBURDEN A a $1 5% NS! w k\ -45 SHALE BED as v 'l l A Y 43 w m INVENTOR' United States Patent i UNDERGROUND SHALE RETORTING PROCESS John W. Scott, Jr., Ross, Califl, assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware Application March 14, 1955, Serial No. 493,937

14 Claims. (Cl. 262-1) This invention relates to a process for recovering volatilizable constituents from carbonaceous materials such as shales, oil and tar sands, coals and the like, by treating such materials in their natural position. More particularly, the present invention is concerned with a process for the in situ retorting of oil shale to recover shale oil.

It is well known that these carbonaceous materials may be converted by a pyrolytic treatment-to yield hydrocarbon oils, including oils boiling in the gasoline and gas oil ranges. Although oil shale does not in general contain oil as such, it does contain volatile and fixed-carbon compounds, termed kerogens, which, upon retorting or destructive distillation, yield products which may be refined much as crude petroleum is to yield fuels and the like.

In the past these shales have generally been mined by methods adopted from the coal industry, crushed, and subjected to destructive distillation in cumbersome external retorts involving large equipment and operating cost. Time consuming handling and crushing operations have contributed to the disadvantages attendant to such a retorting method. In order to avoid the mining and equipment problems of these above-ground special retorts, it has been suggested that the shale be retorted in situ, generally by passing a combustion-supporting gas through a tunnel arrangement within the shale strata, igniting the gas so that the kerogenic material is decomposed by heat, and then recovering the volatile shale oil.

An object of the present invention is to provide a process for recovering oils from carbonaceous materials without extensive mining and handling operations required by most of the retorting processes disclosed in the prior art.

A further object is to provide an improved in situ process for the retorting of shale in which the maximum recovery of oil per unit quantity of shale is obtained and the oil recovered is in suitable form for further processing.

A still further object is to provide a thermally efficient underground oil shale retorting process which provides a stable and controllable means of retorting at relatively low temperatures with the maximum recovery of heat from the retorted products, the spent shale, and the combustion of the retorting fuel gas.

Other objects will be apparent from a consideration of the description below.

The large deposits of oil shales of the United States, particularly in Colorado, Utah and Wyoming, which contain contiguous strata of shales ranging from twenty-five to six hundred feet in thickness, are well suited for the practice of the present invention. The subject invention is particularly applicable to those shale formations which outcrop on the slopes and cliffs above the valleys and which appear between strata of impervious rock and which extend in horizontal beds far back in the sides of the valleys.

According to the present invention, the subject process comprises the steps of employing or forming channels within the carbonaceous material which will permit the passage of fluids through the material. A gaseous fuel is then passed into these channels from a fuel release point, and a combustion zone is established at a predetermined position downstream in the direction of gas flow from said fuel release point, within at least one of the channels, by releasing an oxygen-containing gas at the said position. The combustion zone is at a temperature suflicient to initiate retorting of the carbonaceous material in a retorting zone thereby developed further downstream. The hot retort gases emerging from the retorting zone are then allowed to flow onward through channels in unretorted shale, the cold downstream portions of said channels comprising a condensing zone, thence into a separator from which the normally liquid constituents are recovered and from which at least a'portion of the uncondensed product gases are returned as the gaseous fuel to the channels at the fuel release point. The oxygen-containing gas release point is then progressively advanced through the channels in the direction of the gas flow to effect a corresponding movement of the combustion zone as the carbonaceous material adjacent the zone becomes depleted of volatilizable constituents.

The invention may be more readily understood by reference to the attached drawings wherein:

Figure 1 shows one embodiment of the present invention adapted to retort the oil from a stratum of oil shale outcropping from a clifi, said figure being a vertical section through the clifi formation.

Figure 2 illustrates another embodiment of the invention, the figure being a vertical section through a mountain containing a horizontal stratum of oil shale.

Figure 3 illustrates still another embodiment of the invention, in which valved branch lines are provided, communicating between the recycle gas line 47 and horizontal tunnel 43.

Figure 4 illustrates an inductor-type burner, for use in the present invention.

. Referring to Figure l, the carbonaceous deposit (shown as shale bed 11) to be retorted is located between overburden 12 and country rock 13. According to this embodiment of the present invention, an essentially horizontal tunnel 14 is driven immediately below the oil shale strata 11. A plurality of holes 15, here shown to be vertical, are drilled or otherwise formed between the earths surface 16 and the tunnel 14. Tunnel 14 and holes-15 constitute channels through which fluids may flow.

To start the process, a combustion zone is established within the shale bed 11, preferably at the upper level of the strata. This can be done by passing a fuel gas down the holes from lines 17 and caps 18 and releasing an oxygen-containing gas, for example, air, into theholes by means of lines 20 at the predetermined upper level. A portion of the fuel gas, admixed with the air, in, for

example, a combustion chamber, is then ignited by conventional means, as for example, by an electric spark. The combustion zone thus established must produce sufiicient heat output to initiate retorting of the adjacent shale formation. Following the establishment of the combustion zone, the flow of air and gaseous fuel into the holes is continued so as to support the combustion zone located in the bed. This is accomplished by continuing the passage of the fuel down the holes from lines-17 and caps 18 (the latter being a fuel release point), and the air by header 19 and lines 20, the latter releasing the air at the combustion zone at a predetermined position. The ends of lines 20 may be extended down holes 15 to said predetermined position by any suitable conventional means, for example, by lowering the structure comprising header 19 and lines 20, by making lines 20 of telescopic construction, or by making a portion of lines 20 of flexible, heat resistant material of adequate length to permit lowering said lines to the desired depth. The gases and vaporous products of retorting thereafter flow downwardly the heated gas come in contactwith the shale.

through the holes 15, successively heating thedownstream shale and being cooled thereby to the point where shale oil condenses out. The cold, downstream portion of holes 15 wherein .shale oil is condensed co mprises a condensing zone. The cooled shale oil and product gases pass from the holes into the tunnel 14, or, as shown in the drawing, into a recovery line 21, from which they are passed into separator 22 wherein any remaining vaporous shale oil is condensed, fogs are broken and theliquid phase removed as a product by line 23. The uncondensed gases from retorting, containing'combustion gas, are withdrawn from separator'22 by line 24and' aportion of these gasesmay beremoved from the system by line 25. The remaining retort gases pass by line 24 to blower 26 from which they are passed through line"27, lines 1'7, and caps 18, into holes 115 wherelthey' can replace the 'gase'ousfuel employed to initiate retorting;

Operation of the presentinventio'n after retortingin the shalehas'progressed to 'a' point sufficient tofd isplace gas initially in the system, and after considerable quantities of, retort gas are produced, is as follows.

Cold, recirculated retort gas is passed through line 27, I

lines 17,'and caps 18 into holes 15. The cold-gas passes downwardlyin the holes and comes into contact with hot, previously retorted shale, thereby cooling the shale and heating the gas. These previouslyretor'ted"sections of holes 15 comprise a preheating zone. LA portion" of this preheated gas is withdrawn from the main stream, for

example, by an aspirationror induction device, and is mixed with air entering the holes by header 19 and lines 20 to form a lean fuel/air mixture in respect to its retort g'as content. An important feature of thev present. invention is that the air entering the holes is not mixed with therecycle retortgas at the earths surface 16. Instead, the air is introduced into .the'holes by lines 20' and 7 no mixture 'of air'and recycle gas is made until a point immediatelyabovee. the shale undergoing retorting. The

a lean mixture is burned and a combustion zone wherein a flame temperature considerably above retortingte rnperatures, for example, in the order of 20003000 F., is attained. These high temperature combustion products are immediately admixed with the main stream of circulating retort gas and thus are quenched to a. tem- 'perature of,,for example, 1300 to 1600 R, which is sufficiently above .the desired retorting temperature of from about 1000 to 1250 F. to provide an adequate thermal driving force. of air necessary to be supplied to the process can be as low as 1000 to 2000 cu. ft. per ton of raw shale in certain cases.f

V In the combustion stage, it is preferred in some cases that the combustion take place substantially out 'ofc'ontact with the shale, and that only after quenchingdoes The determining factors are whether clinkering is desired 'to aid in opening channels through the shale, or whether high temperatures are undesirable for process reasons dis cussed subsequently. One means of effecting this combustion out of contact with shaleis to employ an inductor type of burner such as will be discussed in connection with Fig. 4, located on the lower end of air line 20, wherein a portion of the recycle retort gas is inducted or inspirated 'into the burner and mixed with the air to form a lean combustion mixture. "It willbe understood that whether or not aninductor-type of burner is used, that portion of 'the' stream of recycle retort gas passing into holes 15 It has been found that the amount present invention, by preventing the flame front-from from caps 18 that is not burned near the end of line 20 inherently acts asa thermal cushion between the combustion zone and the shale walls of holes 15. This thermal cushion may be used, in conjunction with a combustion zone designed to have a flame front with a desired direction and configuration, to prevent the flame "an outside source.

' The hot recycle gas passes downwardly from the cornbustion zone and heats downstream shale to retorting temperature thereby converting the kerogenic materials therein to vaporized shale oil. The region in which this is the dominant reaction is termed the retorting zone. .The recycle gas and the hot gaseous products of retorting then pass further down the holes, preheating the raw shale as they are being cooled. The region in which the gases and vapors are cooled by contact with raw shale is termed the condensing zone. These gases may be cooled by their passage through the raw shale to a point at which condensation of the shale oil occurs, but in any case, the gases, or gases and liquid shale oil, are passed from the holes 15 through the tunnel 14, or recovery line 21, into separator 22 wherein essentially all of the vaporous shale oil is recovered as a liquid. At least a portion of the uncondensed gases from the condensing zone, constituting recycle gas, are then returned by line 24-through blower 'to recover sensible heat therefrom. 'This effects a large improvement in thermal etficiencyand also permits the use of low-B. t. u. gases as fuels, since these must be preheatedbefore combustion can proceed satisfactorily.

Other advantages of the present-invention are as follows:

1. Except for the unusual instance of retorting with electric energywhich-is uneconomic in most parts of the world, all of the heat requirements for retorting must be generated by the combustion of hydrocarbons retorted from the shalefresidual in the shale, or introduced from The heat requirements for retorting include the sensible heat required to, bring the shale and circulating gas up to retorting temperature, plus the heats of decomposition of shale, kerogen and oil, and of any carbonate mineral in theshale. Operation with the maximum' heat recovery results in'the increased recovery of hydrocarbons froma unit quantity of shale with the attendant decrease in cost per'unit quantity of hydrocarbons. 'Thus, in the present invention, by contacting the recirculating retortgas with the hot'spent shale, and by heating the 'raw downstream shale with the retor products, maximum heat recovery is attained.

2. Since retorted shale oil must be reduced in molecular weight before final product separation, the avoidance of unnecessary cracking of shale oil during retorting permits the later use of refining processes such as thermal and catalytic cracking, operated under carefully controlled conditions, to give maximum yields of productswithin the desired gasoline and gas oil boiling ranges. In the actually contacting the shale, the high cracking temperatures are avoided resulting in a shale oilproduc boiling within the desired ranges.

3. Another advantage of the present process is that by operating at relatively low temperatures, that is by.

a shielded'fiame followed by gas quenching, the retort gas will be of a relatively high molecular Weight,- and thus, the molal'heat capacity of the gaseous fuel'is maintained 'at'a higher level than would be the case when excessive temperatures are-employed, the latter giving rise to low molecular weight product gases produced by thermal V cracking. The higher'the m'olal heat capacity of the gas, the less gas must bebrought into contact with-the shale to effect retorting," thus reducing the cost of gas compressionto bring-the gas into contact withthe shale.

4. A further advantage of the shielded flame followed by quenching, is that a minimum breakdown of carbonate compounds, often contained in shale, results because of the avoidance of high temperature flame contact with the shale. A disadvantage of carbonate decomposition is that carbon dioxide will be released, in an endothermic reaction wasting heat, diluting the normally gaseous hydrocarbon products with carbon dioxide and decreasing their heating value. The consequence of low heating value fuel gas is a reduced thermal efliciency in any combustion process in which it is used.

5. A still further advantage of the present invention is that the process provides the most eflicient type of combustion, i. e., a lean gas-air mixture with a high flame temperature. This is obtained by inducting recycle retort gas into the oxygen-containing stream being passed into the holes, and burning under these lean conditions. As a result of this feature, a maximum amount of heat is liberated per unit volume of circulated gas, and dilution of the retort gas with inerts is held to a minimum. This still further conserves its heating value over 4 above.

Another embodiment of the present invention is illustrated in Figure 2, wherein shale bed 40 is located between overburden 41 and country rock 42. Pursuant to the invention, tunnels 43 and 44 are driven into the shale bed so that a body of the shale lies between the two tunnels, the latter being driven so that the upper tunnel 43 is essentially parallel to and superimposed over the lower tunnel 44. As shown in the figure, the tunnels are driven at the upper and lower extremities of the shale bed 40, but it must be understood that if the bed is extremely thick, it may be desirable only to isolate a portion of the shale between the tunnels. If such be the case, it may also be desirable to etfect retorting of the stratum by employing a plurality of these systems hereinafter described.

'Following the establishment of tunnels 43 and 44, a

plurality of essentially vertical holes 45 are drilled or otherwise formed in the shale between the two tunnels, the tunnels and holes constituting channels. A plurality of bafiies 46 are positioned at predetermined positions in each of the horizontal tunnels 43 and 44 in such a manner as to provide alternate zones of downward and upward fiow through the vertical holes 45 in the shale bed.

A combustion zone is established at a predetermined position in the first of these alternate zones by releasing at a fuel release point a hot fuel gas which is passed into the formation through line 47, and by releasing at said predetermined position downstream an oxygen-containing gas, preferably air, which is passed into the first zone by header 48 and line 49. Header 48 is provided with branch lines 49, 50, 51, 52, and 53, each of which is equipped with a valve, the valves numbered 54, 55, 56, 57, and 58, respectively. Initial operation is conducted with only valve 54 in line 49 open, the remaining valves in the branch lines being closed. After the combustion zone, having a temperature in the range of from about 800 to 1600 F., is established and maintained by the fuel gas and oxygen-containing gas introduced as described, the hot gaseous products of retorting thereafter alternately flow downwardly and upwardly through the vertical holes 45 in each zone of the shale bed, preheating the downstream shale and in turn being cooled by their passage. During the passage of these retort gases through the downstream shale, they may be cooled to such a degree that the shale oil will condense partially as a liquid and partially in the form of a fog, the latter being carried along by the product gases. These cool, downstream sections form a condensing zone. The disposition of the shale oil liquid and fog may be accomplished in several ways. One method is to merely pass the total liquid-foggas products through the alternate Zones and removing them through tunnel 44 into separator 59 wherein cssentially all of the normally liquid shale oil is recovered as a liquid from line 60. A preferred method of recovering the liquid-fog-gas product is shown in the figure. In this method, when the liquid shale oil is condensed out of the retort gases by contact with cold downstream shale, the liquid product can be recovered from each alternate zone by a valved arrangement of product lines. Thus, the first shale oil will condense out in the first zone and can be removed via product line 61. This latter line is equipped with branch lines 62, 63, and 64 which connect each zone with the product line 61. Line 61 is provided with a valve 65 and the branch lines are similarly equipped with valves 66, 67, and 68 respectively. Thus, when the liquid shale oil forms in the first zone, only valve 65 will be open, which allows the liquid to pass through line 61 into line 60. As will be seen by the description below, the retorting will progress through the downstream zones, with the attendant shale oil condensation occurring downstream of the zone undergoing retorting, and thus, this liquid may be recovered by merely opening the valve in the product branch line where the liquid is formed, and collecting it through line 61.

During the preferred liquid recovery method described above, the fog-gas mixture may be allowed to flow through the downstream zones into the separator 59, or, in order to conserve horsepower, the mixture can be removed by means similar to that employed in the liquid recovery system. Thus, the mixture can be removed by header 69 (equipped with valve 70) and branch lines 71, 72, and 73 provided with valves 74, 75, and 76 respectively, which pass the mixture into the separator 59. For example, upon the formation and withdrawal of liquid shale oilin the first zone, it is not necessary to flow the fog-gas mixture through the entire mountain, but it may be directly re moved from the second zone (by branch line 71 and line 69 with valve 74 open) or any other downstream zone. Operating in this manner will considerably reduce the horsepower that would be necessary if the mixture was to be forced through all of the downstream zones. Of course, the liquid and fog-gas recovery methods described may be altered in various ways, such as by employing a single recovery line, or by reducing or increasing the number of branch lines, but these are all within the scope of the present invention and apparent to those skilled in the art.

Whatever recovery methods are employed, from the separator is discharged the liquid product by line 60, and at least a portion of the uncondensed retort gases, con stituting recycle gas, are then returned by line 77, blower 78, and line 47 to the fuel release point in the first alternate zone. The remaining portion of the gases may be withdrawn from the system by line 79 and used as a fuel gas elsewhere.

Operation of this embodiment of the invention, after establishment of the combustion zone and retorting of the shale has progressed to a point sufficient to displace the air in the system, is as follows.

Cold recycle retort gas is passed through line 77, blower 78, and line 47 and is released at the fuel release point in the first zone. The cold gas passes through the first zone, contacting hot, previously retorted shale (comprising a preheating zone), thereby cooling the shale and heating the recycle gas. A portion of this preheated gas is withdrawn, for example by an induction device: and is mixed with an oxygen-containing gas, preferably air, entering the system by header 48 and branch line 50. The air is introduced by line 50 for the following reasons. Since an important aspect of the present invention is to release the oxygen-containing gas at the combustion zone, thereby preventing the disadvantages heretofore pointed out, the passing of the air into the depleted first zone is avoided, and thus, the air is introduced so as to support a combustion zone downstream from the previously retorted shale and upstream from the zone of active retorting which is proceeding through the shale. Thus, valve 55 other modificationof the presentinvention is to provide the recycle retort gas return'line '47 of Figure 2 with valved branch lines .85, having .valve si' o, similar to the valved branch linesin the air-inlet system. Only so much of the pertinent portions of Fig. 2 are reproduced in Fig. 3 as are. necessary toillustrateihis modification. in such an'operation, the'recycle gas is injected into hot depleted zones upstreamfro'm the combustion zone; For example, as the retorting progresses through the stratum, the initi- -ally retorted shale zones will be cooled to a point where the recycle gases will not be appreciably heated by their passage and no advantage would be gained by passing them ona tortuous path through the cold depleted zones. Thus, by a header-branch line arrangement, the recycle gas can be returned only to hot retorted zones, thereby being preheated. However, in such 'an operation, the recycle gas is introduced only to zones upstream from the combustion zone. V

The terms induction device,and inductor-type'bu'rner used herein refer to a burner well known in the art,

'viz', one in which a stream of a first gas in passing through the burner under pressure exerts an aspirating effect:to draw a second gas into contact with the first gas. The common Bunsen burner, is anexample of an air-induction burner; A gas-induction burner operating on similar principles is recommended for use in the present invention. Such a burner is exemplified in Fig. 4. Referring now to Fig. 4, burner body 87*isattached to air inlet pipe 88. The end of pipe 88 is preferably reduced in diameter as shown as necessary to provide an air jet of the desired velocity. This air jet enters body 87 along with combustible gas that it inspirates through apertures 99; The amount ofinspirated gas, and thus the leanness of the gas air mixture, may be controlled in various ways, for example,"by varying the'size and number of apertures 96. The'sloping sides91 of body 87 may be designed to serve asflame shields or directors to keep the flame front from contacting adjacent shale; in addition to forcing the inspirated gas into mixing contact with the air stream emerging from pipe 38. It will be appreciated that an inductortype burner'is only one possible means for effecting the combustion necessary in this invention, and that those skilled in the art will be aware of other means for creat ing a combustion zone in the proper proximity to the shale. i

While the process described herein has been directed primarily to the retorting of oil shale, it must be understood that the process is adaptable for the recovery of oil from any subterranean oil-containing substance. The present invention employs the word channels to denote either artificially created fluid passageways such as tunnels, drilled holes, the void spaces resulting from stoping or fracturing, or the naturally occurring fluid passageways that'exist in porous media or the interstitial spaces present in oil sands and the like. t is particularly intended that the retorting of shale oil from fractured shale contained in underground stopes is within the scope of the present invention. V

I claim 1. A process of recovering volatilizable constituents from underground formations of'carbonaceous material, said materials containing'channels capable of permitting fluid flow therethrough, said channels having substantially exposed walls of 'said'carbonaceousmaterial, which comprises passing a gaseous fuel into'said'channels from a fuel release point;' establishing. a combustion zone-at a predetermined position withinat least oneof said channels downstream from said fuel release point by releasing an oxygen containing gas at said position; passing the resulting gaseous and'vap'orous products of retorting'and combustion through said channels, into a separator; recovering the normally liquid constituents from saidsepara tor and returning at least a portion of the uncondensed prod-- uct gases as the gaseousfuel to said channels at said'fuel release point; andprogressively advancing the release .point of said oxygen-containing gas in the direction of gas flowin said channels to effect a corresponding movementlof said combustion zone, as, the adjacent carbona- "ceous material becomes depleted of volatilizable constituents. V f I p 2. The process of claim 1 wherein the fuel release point is progressively advanced in the direction of gas flow'in said channels, said fuel release point being always maintained upstream of said combustion zone, so as to contact the gaseous fuel with hot, previously retorted carbonaceous material.

3. The processof claim 1 wherein the carbonaceous material is oil shale.

4. A process of recovering volatilizable constituents from carbonaceous material in its'natural position, which comprises driving an essentially horizontal tunnel immediately below said material; drilling a plurality of substantially vertical holes through said material into said tunnel, said holes having substantially exposed walls of said carbonaceous material; passing a gaseous fuel through 7 level Withineach of said holes downstream from said fuel release point by releasing an oxygen-containing gas at said upper level; passing the resulting hot gaseous and vapoorus products of retorting and combustion through said holes and said tunnel into'a separator; recovering the normally liquid constituents from said separator and returning at least-a portion of the uncondensed products as' the gaseous fuel-to said holes at said fuel release point; and releasing said oxygencontaining gas at progressively lower levels in said holes to effect a corresponding lowering in said combustion zone as the adjacent carbonaceous material becomes depleted of'volatilizable constituents.

stantially exposed walls of said carbonaceous material;

positioning a plurality of baflies at predetermined points within each of said tunnels to provide interconnecting alternate zones of up and down flow through a series of the vertically drilled holes between said tunnels; releasing a gaseous fuel into the first of said zones adjacent .the exterior of said material from' a fuel release point;

establishing a combustion zone at a predetermined position within said first zone downstream from said fuel release point by releasing an oxygen-containing gas at said position; passing the resulting hot gaseous and vaporous products of retorting and combustion alternately up and ,down through the remaining interconnecting zones into a separator; recovering the normally liquid constituents from said separator and recycling at least a portion of the uncondensed products as the gaseous fuel 'into said first interconnecting zone at said fuel release point; and progressively advancing the release point of said oxygencontaining gas through the remaining downstream alternate zone's to etfect'a corresponding movement of said combustion zone as the adjacent carbonaceous material becomes depleted of volatilizable constituents.

7. The'pr'o'cessof'claim 6 wherein the fuel release point is progressively advanced in the direction of gas flow through said downstream alternate zones, said fuel release point being always maintained upstream of said combustion zone, so as to contact the gaseous fuel with hot, previously retorted carbonaceous material.

8. The process of claim 6 wherein the carbonaceous material is oil shale.

9. The process of claim 6 wherein the combustion zone is established at said predetermined position by withdrawing a portion of the main stream of gaseous fuel passing through the interconnecting zones and m'ming said portion with an oxygen-containing gas, said latter gas being released at said predetermined position, burning the resulting mixture, and passing the resulting combustion products into said main stream of gaseous fuel.

10. The process of claim 9 wherein the gaseous fuel/oxygen-containing gas mixture is substantially at the stoichiometric ratio for combustion.

11. A process of recovering volatilizable constituents from underground formations of carbonaceous material, said material containing channels capable of permitting fluid flow therethrough, which comprises passing a main stream of gaseous fuel into said channels from a fuel release point; establishing a combustion zone at a predetermined position within at least one of said channels downstream from said fuel release point by releasing an oxygen-containing gas at said position; passing the resulting gaseous and vaporous products of retorting and combustion through said channels into a separator; recovering the normally liquid constituents from said separator and returning at least a portion of the uncondensed product gases as the gaseous fuel to said channels at said fuel release point; progressively advancing the release point of said oxygen-containing gas in the direction of gas flow in said channels to effect a corresponding movement of said combustion zone as the adjacent carbonaceous material becomes depleted of volatilizable constituents; and establishing said combustion zone at said predetermined position by withdrawing a portion of said main stream of gaseous fuel passing through said channels and mixing said portion with said oxygen-containing gas released at said predetermined position, burning the resulting mixcore, and passing the resulting combustion products into said main stream of gaseous fuel.

12. The process of claim 11 wherein the gaseous fuel/oxygen-containing gas mixture is substantially at the stoichiometric ratio for combustion.

13. A process of recovering volatilizable constituents from carbonaceous material in its natural position, which comprises driving an essentially horizontal tunnel immediately below said material; drilling a plurality of substantially vertical holes through said material into said tunnel; passing a main stream of gaseous fuel through said holes into said tunnel from a relatively fixed fuel release point; establishing a combustion zone at an upper level within each of said holes downstream from said fuel release point by releasing an oxygen-containing gas at said upper level; passing the resulting hot gaseous and vaporous products of retorting and combustion through said holes and said tunnel into a separator; recovering the normally liquid constituents from said separator and returning at least a portion of the uncondensed products as the gaseous fuel to said holes at said fuel release point; releasing said oxygen-containing gas at progressively lower levels in said holes to effect a corresponding lowering in said combustion zone as the adjacent carbonizable material becomes depleted of volatilizable constituents; and establishing said combustion zone at said upper level by withdrawing a portion of said main stream of gaseous fuel passing through said holes and mixing said portion with said oxygen-containing gas released at said upper level, burning the resulting mixture, and passing the resulting combustion products into said main stream of gaseous fuel.

14. The process of claim 13 wherein the gaseous fuel/oxygen-containing gas mixture is substantially at the stoichiometric ratio for combustion.

References Cited in the file of this patent UNITED STATES PATENTS 1,919,636 Karrick July 25, 1933 2,481,051 Uren Sept. 6, 1949 2,630,306 Evans Mar. 3, 1953 

1. A PROCESS OF RECOVERING VOLATILIZABLE CONSTITUENTS FROM UNDERGROUND FORMATIONS OF CARBONACEOUS MATERIAL, SAID MATERIALS CONTAINING CHANNELS CAPABLE OF PERMITTING FLUID FLOW THERETHROUGH, SAID CHANNELS HAVING SUBSTANTIALLY EXPOSED WALLS OF SAID CARBONEOUS MATERIAL, WHICH COMPRISES PASSING A GASEOUS FLUID INTO SAID CHANNELS FROM A FUEL RELEASE POINT; ESTABLISHING A COMBUSTION ZONE AT A PREDETERMINED POSITION WITHIN AT LEAST ONE OF SAID CHANNELS DOWNSTREAM FROM SIAD FUEL RELEASE POINT BY RELEASING AN OXYGEN-CONTAINING GAS AT SAID POSITION; PASSING THE RESULTING GASEOUS AND VAPOROUS PRODUCTS OF RETORTING AND COMBUSTION THROUGH SAID CHANNELS INTO A SEPARATOR; RECOV-ERILNG THE NORMALLY LIQUID CONSTITUENTS FROM SAID SEPARATOR AND RETURNING AT LEAST A PORTION OF THE UNCONDENSED PRODUCT GASES AS THE GASEOUS FUEL TO SAID CHANNELS AT SAID FUEL RELEASE POINT; AND PROGRESSIVELY ADVANCING THE RELEASE POINT OF SAID OXYGEN-CONTAINING GAS IN THE DIRECTION OF GAS FLOW IN SAID CHANNELS TO EFFECT A CORRESPONDING MOVE- 